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STUDY ON VERTICAL STRUCTURE OF TROPICAL CYCLONES FORMED IN THE BAY OF BENGAL DURING 2007-2016 A dissertation submitted to the Department of Physics, Bangladesh University of Engineering and Technology (BUET), Dhaka in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN PHYSICS Submitted by SHAIYADATUL MUSLIMA Roll No.: 0416142506F Session: April/2016 DEPARTMENT OF PHYSICS BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY (BUET), DHAKA-1000, BANGLADESH April, 2019 i CANDIDATE'S DECLARATION It is hereby declared that this thesis or any part of it has not been submitted elsewhere for the award of any degree or diploma. Signature of the Candidate ---------------------------------------------------- SHAIYADATUL MUSLIMA Roll No.: 0416142506F Session: April/2016 ii iii Dedicated To My Beloved Parents iv CONTENTS Page No. List of Table viii List of Figures ix Abbreviations xv Acknowledgement xvi Abstract xvii Chapter No. Page No. CHAPTER 1: INTRODUCTION 1 1 1.1 prelude 1.2 objectives of the research 2 CHPATER 2: LITERATURE REVIEW 2.1 previous work 4 2.2 Overview of the study 6 2.2.1 Cyclone 6 2.2.2 Detail of tropical cyclone 6 2.2.3 Cyclone season 7 2.2.4 Tropical cyclone basins 8 2.2.5 Bay of Bengal 9 2.2.6 Classifications of tropical cyclone intensity 10 2.2.7 Physical structure of tropical cyclone 11 2.2.8 Environmental parameters related to cyclone 13 2.2.8.1Wind 13 2.2.8.2 Wind shear 14 2.2.8.3 Temperature 15 2.2.8.4 Vorticity 16 2.2.8.5 Equivalent potential temperature 18 2.2.8.6 Relative humidity 18 CHAPTER 3: DATA AND METHODOLOGY 20 3.1 Data Sources 20 3.1.1 JTWC 20 3.1.2 NCEF-CFSR 20 3.2 Study area 21 3.3 Study method 22 3.3.1 Scale used for cyclone intensity 22 3.3.2 Selection of tropical cyclone 23 3.3.3 Used environmental parameters 25 3.3.4 Grads 26 CHAPTER 4: CYCLONES OVERVIEW 4.1 Pre-mosoon cyclones 27 4.1.1 Akash (2007) 27 4.1.2 Nargis (2008) 28 v 4.1.3 Aila (2009) 29 4.1.4 Laila (2010) 30 4.2 Post- monsoon cyclones 31 4.2.1 Sidr (2007) 31 4.2.2 Giri (2010) 32 4.2.3 Phailin (2013) 33 4.2.4 Thane (2011) 34 4.2.5 Vardah (2016) 35 4.2.6 Helen (2013) 36 4.2.7 Madi (2013) 37 4.2.8 Lehar (2013) 38 4.2.9 Hudhud (2014) 39 Chapter 5: Results and discussion 41 5.1 Tropical cyclones in the BoB 41 5.2 Structure of symmetric and asymmetric cyclones 42 5.3 Vertical characteristics of environmental parameters 52 of cyclones 5.3.1 Vorticity distribution and its anomalies 52 5.3.1.1 Pre-monsoon cyclones. 52 5.3.1.2 Post-monsoon cyclones. 55 5.3.1.3 Comparison between pre- and post- 62 monsoon cyclones. 5.3.2 Temperature distribution and its anomalies 64 5.3.2.1 Pre-monsoon cyclones. 64 5.3.2.2 Post-monsoon cyclones. 67 5.3.2.3 Comparison between pre- and post- 74 monsoon cyclones. 5.3.3 Relative humidity distribution and its anomalies 76 5.3.2.1 Pre-monsoon cyclones. 76 5.3.2.2 Post-monsoon cyclones. 79 5.3.2.3 Comparison between pre- and post- 86 monsoon cyclones. vi 5.3.4 Equivalent potential temperature distribution and its 88 anomalies 88 5.3.4.1 Pre-monsoon cyclones. 5.3.4.2 Post-monsoon cyclones. 91 5.3.4.3 Comparison between pre- and post- 97 monsoon cyclones 5.4 Summary of the centre characteristics for pre- and 100 post- monsoon cyclones. 5.5 Vertical characteristics the left and right front 101 Quadrants of cyclones 5.5.1 Vorticity distribution 101 5.5.5.1 Pre-monsoon cyclones 101 5.5.5.2 Post -monsoon cyclones 102 5.5.5.3 Comparison between pre- and post- 103 monsoon cyclones 5.5.2 Relative humidity distribution 105 5.5.2.1 Pre-monsoon cyclones 105 5.5.2.2 Post -monsoon cyclones 106 5.5.2.3 Comparison pre- and post-monsoon 107 cyclones 5.5.3 Temperature distribution 109 5.5.3.1 Pre-monsoon cyclones 109 5.5.3.2 Post -monsoon cyclones 109 5.5.3.3 Comparison between pre- and post- 110 monsoon cyclones. 5.5.4 Equivalent potential temperature distribution 112 5.5.4.1 Pre-monsoon cyclones 112 5.5.4.2 Post -monsoon cyclones 113 5.5.4.3 Comparison pre- and post-monsoon 114 cyclones. vii 5.5.5 Horizontal wind distribution 116 5.5.5.1 Pre-monsoon cyclones 116 5.5.5.2 Post -monsoon cyclones 117 5.5.5.3 comparison between pre- and post- 118 monsoon cyclones 5.5.6 Zonal component of wind distribution 121 5.5.6.1 Pre-monsoon cyclones 121 5.5.6.2 Post -monsoon cyclones 122 5.5.6.3 Comparison between pre- and post- 122 monsoon cyclones 5.5.7 Meridional component of wind distribution 125 5.5.7.1 Pre-monsoon cyclones 125 5.5.7.2 Post -monsoon cyclones 126 5.5.7.3 Comparison between pre- and post- 127 monsoon cyclones 5.5.8 Wind shear between 1000-850 hPa and 850-200 hPa 129 5.6 Summary of the left and right quadrants of tropical 130 cyclones Chapter 6: Conclusions and Future prospect 133 Reference 137 Appendix 141 List of Tables No. Caption Page No. Table 2.1 Tropical Cyclone Intensity Scale according to IMD 11 Table 3.1 Tropical Cyclone Intensity Scale according to IMD 23 Table 5.1 Tropical cyclones formed over the BoB from 2007-2016 41 with their intensities. Table 5.2 Maximum intensity with time of 65 kt for 13 cyclones 42 Table 5.3 Summary of relative vorticity at the centre core of pre- 64 and post-monsoon TCs. Table 5.4 Summary of temperature at the centre core of pre- and 76 post-monsoon TCs. viii Table 5.5 Summary of relative humidity at the centre core of pre- 88 and post-monsoon TCs. Table 5.6 Summary of equivalent potential temperature at the 99 centre core of pre- and post-monsoon TCs. Table 5.7 Summary of vertical distribution of atmospheric 100 parameters along the centre of TCs. Table 5.8 Summary of relative vorticity in the left and right 104 quadrants of TCs . Table 5.9 Summary of relative humidity in the left and right 108 quadrants of TCs . Table 5.10 Summary of temperature in the left and right quadrants 112 of TCs . Table 5.11 Summary of equivalent potential temperature in the left 116 and right quadrants of TCs . Table 5.12 Summary of horizontal wind in the left and right 120 quadrants of TCs . Table 5.13 Summary of zonal component of wind in the left and 124 right quadrants of TCs . Table 5.14 Summary of meridional component of wind in the left 128 and right quadrants of TCs . Table 5.15 Characteristics of vertical wind shear between 1000- 129 850 hPa and 850-200 hPa for left and right quadrants of pre-monsoon and post-monsoon cyclones. Table 5.16 Summary of vertical distribution of atmospheric 130 parameters in the left and right side of pre- and post- monsoon cyclones. List of Figures No. Caption Page No. Fig 2.1. View of tropical cyclone 7 Fig 2.2. (a) Tropical cyclone formation over the Bay of Bengal (BoB) 8 during 1990–2009 (dots): red pre- monsoon; black post-monsoon; ix green other. (b) Annual cyclone occurrence frequency Fig 2.3. Tropical cyclone formation probability basins 9 Fig 2.4. Location of the Bay of Bengal 10 Fig 2.5. A cross section diagram of a mature tropical cyclone. 13 Fig 2.6. Effects of VWS on tropical cyclone 15 Fig 2.7. Seasonal peaks of tropical cyclone activity worldwide in terms of 16 sea surface temperature. Fig 2.8. Earth Vorticity 17 Fig 2.9. Cyclonic and anticyclonic phase of vorticity 17 Fig 3.1. Location map of study area (BoB) 22 Fig 3.2. Total number of tropical cyclones over BoB during 2007-2016 24 Fig 3.3. Vertical structure of TC 25 Fig 4.1. JTWC track of cyclone Akash-2007 28 Fig 4.2. JTWC track of cyclone Nargis-2008 29 Fig 4.3. JTWC track of cyclone Aila-2009 30 Fig 4.4. JTWC track of cyclone Laila-2008 31 Fig 4.5. JTWC track of cyclone Sidr-2007 32 Fig 4.6. JTWC track of cyclone Giri-2010 33 Fig 4.7. JTWC track of cyclone Phailin-2013 34 Fig 4.8. JTWC track of cyclone Thane-2011 35 Fig 4.9. JTWC track of cyclone Vardah-2016 36 Fig 4.10. JTWC track of cyclone Helen-2013 37 Fig 4.11. JTWC track of cyclone Madi-2013 38 Fig 4.12. JTWC track of cyclone Lehar-2013 39 Fig 4.13. JTWC track of cyclone Hudhud-2014 40 Fig 5.1. (a) Mean sea level pressure (hPa) and horizontal wind (ms-1) at 43 850 hPa (b) the vertical cros-section of maridional wind (ms-1) component for cyclone Akash (2007). Fig 5.2. (a) Mean sea level pressure (hPa) and horizontal wind (ms-1) at 44 850 hPa (b) the vertical cros-section of maridional wind (ms-1) component for cyclone Nargis (2008). Fig 5.3. (a) Mean sea level pressure (hPa) and horizontal wind (ms-1) at 44 850 hPa (b) the vertical cros-section of maridional wind (ms-1) component for cyclone Aila (2009).